This invention relates to a printing plate, a method of making a printing plate, and a method of printing using a printing plate to form a desired image on a medium. More particularly, the printing plate of this invention employs a substrate and a fluid composition comprising a cationic polymer and an anionic polymer, in which the ionic polymers interact and adhere to the substrate. The fluid composition is applied by ink jetting to the substrate, providing a printing plate that is ready-to-use on a press without having to develop it.
The offset lithographic printing process has long used a developed planographic printing plate having oleophilic image areas and hydrophilic non-image areas. The plate is commonly dampened before or during inking with an oil-based ink composition. The dampening process utilizes a fountain solution such as those described in U.S. Pat. Nos. 3,877,372, 4,278,467 and 4,854,969. When water is applied to the plate, the water will form a film on the non-image hydrophilic areas, but will contract into tiny droplets on the oleophilic image areas. When a roller carrying an oil-based ink composition is passed over the dampened plate, it will not ink the non-image areas that are covered by the aqueous film, but will emulsify the water droplets on the water repellant image areas, which will then take up ink. The resulting ink image is transferred, or xe2x80x9coffset,xe2x80x9d onto a rubber blanket, which is then used to print onto a medium such as paper.
It has been proposed to apply xe2x80x9cdirectxe2x80x9d ink jet printing techniques to lithographic printing. For example, European Patent Publication No. 503,621 discloses a direct method to make lithographic plates by jetting a photocurable ink onto the plate substrate, and then exposing the plate to ultraviolet radiation to harden the image area. An oil-based ink may then be transferred to the image area for printing onto a printing medium. But, neither the resolution of ink drops jetted onto the substrate, nor the durability of the lithographic printing plate with respect to printing runlength was disclosed.
It has also been proposed to apply the direct ink jet printing techniques without the additional steps of chemical development of the plate. This approach advantageously results in lower production costs and a more environmentally acceptable printing process. However, in such techniques it is difficult to control the spreading of the droplets of ink-jetted fluid that forms the oleophilic ink-accepting regions on the printing plate substrate. Such droplet xe2x80x9cdot spreadingxe2x80x9d causes lower resolution of printed images and reduced image quality. For example, European Patent Application No. 591,916 A2 discloses a water-based ink having a polymer containing anhydride groups which are thermally cross-linked on the substrate with a hydroxy-functional polymer. This formulation is applied by jetting the formulation, which is at room temperature, onto a room temperature substrate. However, this formulation does not achieve good control of dot spreading.
U.S. Pat. No. 4,833,486 discloses the apparatus and process for imaging a plate with a xe2x80x9chot meltxe2x80x9d type of ink jet printer. The image is produced by jetting at high temperature a xe2x80x9cphase changexe2x80x9d type of ink which solidifies when it hits the cooler substrate. The ink becomes instantaneously solid rather than remaining a liquid or gel which is thereafter cured to form a solid. However, such an ink does not provide good resistance to press run due to the wax-type nature of the ink formulation.
U.S. Pat. No. 5,942,335 discloses the use of a polymer containing a nitrogen-containing heterocyclic group, namely a polymer of 4-vinyl pyridine, in the formulation of an ink receiving layer of an ink jet recording sheet. However, the use of such a compound in a fluid composition applied directly to a printing plate substrate to form an imaged, ink-receptive layer is not disclosed.
Thus, it would be advantageous to employ a printing plate capable of extended press run length which does not require chemical development.
It is one object of this invention to provide such a printing plate. It is another object of this invention to provide a method of preparing such a printing plate. It is yet another object of this invention to provide a method of using such a printing plate. The printing plate of this invention may advantageously be prepared without a chemical development step typically required. The printing plate of this invention is also capable of extended press run length.
The fluid composition of this invention is suitable for ink jetting upon a substrate and comprises a cationic product polymer and an anionic product polymer, in non-aqueous solvent. The ionic product polymers interact and adhere to the substrate, so that after drying, a durable printing plate is formed without chemical development.
The printing plate of this invention is prepared by: (a) providing a substrate; and (b) applying by ink jetting to the substrate a fluid composition as described below. In a preferred embodiment, the substrate is pretreated with a surfactant to provide a printing plate precursor.
In preferred embodiments, the cationic product polymer is prepared from a basic polymeric compound which is selected from the group consisting of polymers and copolymers of 2-vinylpyridine, polymers and copolymers of 4-vinylpyridine, polymers and copolymers of dimethylaminoethyl methacrylate, and mixtures or derivatives thereof. The basic polymeric compounds prepared from these monomers are made cationic by at least partially neutralizing with an acid, preferably formic acid, to create cationic conjugate acid groups from the base groups of the basic polymeric compounds.
In preferred embodiments, the anionic product polymer is prepared from an acidic polymeric compound which is selected from the group consisting of poly(acrylic acid)s, poly(methacrylic acid)s, poly(maleic acid)s, poly(maleic anhydride)s, poly(fumaric acid)s, poly(styrene-co-acrylic acid)s, poly(styrene-co-maleic acid)s, poly(styrene-co-fumaric acid)s, and mixtures or derivatives thereof. These acidic polymeric compounds are made anionic by at least partially neutralizing with base, preferably ammonia, to create anionic conjugate base groups from the acid groups of the acidic polymeric compounds.
The printing plate of this invention is capable of extended press run length and advantageously avoids the need of chemical development.
To achieve extended printing runs with lithographic plates the oleophilic material must adhere well to the substrate. Adhesion of the oleophilic material may be controlled in at least two ways. First, the oleophilic material should have a chemical interaction with the substrate that provides a type of chemical binding and promotes adhesion. For example, the chemical composition of the oleophilic material can be varied to promote its adhesion to the substrate. Also, the composition of the substrate can be varied to increase binding of the oleophilic material. Further, high cohesive strength of the oleophilic material helps to bind it to itself on the substrate, thus improving its adhesion. Cohesive strength of the oleophilic material is enhanced by providing a means for chemical interaction between the molecules of the oleophilic material, preferably by crosslinking.
The second way that adhesion of the oleophilic material may be controlled is by providing a substrate in which microscopic topology allows the oleophilic material to interlock mechanically with the substrate when dry or hardened. Mechanical interlocking can be affected by roughening the surface of the substrate. Thus, by controlling these variables, a printing plate can be made with increased adhesion of the oleophilic material, and correspondingly longer printing run operation.
In the invention described here, the oleophilic material is placed on the substrate by ink jetting a fluid composition comprising the oleophilic material. Optionally, by pretreating the substrate surface with a surfactant to lower its surface tension, the spreading of droplets of fluid composition is reduced. Thus, by these and other features inherent in the composition and method described here, excellent printing resolution can be obtained, as well as long-lasting adhesion of the dried oleophilic material to the substrate.
The printing plate of this invention encompasses lithographic printing plates, flexographic printing plates, and gravure printing plates.
Conventional printing plate substrates such as aluminum, polymeric film, and paper may be used as the printing plate substrate of this invention. The printing plate substrate may be subjected to treatments such as electrograining, anodization, and silication to enhance its surface characteristics. The surface characteristics that are modified by such treatments are roughness, topology, and the nature and quantity of surface chemical sites.
Substrates that can be employed are given in Table 1. Substrates chosen for use in this invention are preferably based on aluminum oxide, and may be subjected to various conventional surface treatments as are well known to those skilled in the art, and give a surface that has either acidic or basic character in the Bronsted acid-base view. These treatments also result in different surface roughness, topology, and surface chemical sites, as summarized in Table 1.
xe2x80x9cAAxe2x80x9d means xe2x80x9cas anodized.xe2x80x9d The aluminum surface is first quartz grained and then anodized using DC current of about 8 A/cm2 for 30 seconds in a H2SO4 solution (280 g/liter) at 30xc2x0 C.
xe2x80x9cEGxe2x80x9d means xe2x80x9celectrolytic graining.xe2x80x9d The aluminum surface is first degreased, etched and subjected to a desmut step (removal of reaction products of aluminum and the etchant). The plate is then electrolytically grained using an AC current 30-60 A/cm2 in a hydrochloric acid solution (10 g/liter) for 30 seconds at 25xc2x0 C., followed by a post-etching alkaline wash and a desmut step. The grained plate is then anodized using DC current of about 8 A/cm2 for 30 seconds in a H2SO4 solution (280 g/liter) at 30xc2x0 C.
xe2x80x9cPVPAxe2x80x9d is a polyvinylphosphonic acid. The plate is immersed in a PVPA solution and then washed with deionized water and dried at room temperature.
xe2x80x9cDSxe2x80x9d means xe2x80x9cdouble sided smooth.xe2x80x9d The aluminum oxide plate is first degreased, etched or chemically grained, and subjected to a desmut step. The smooth plate is then anodized.
xe2x80x9cSilxe2x80x9d means the anodized plate is immersed in a sodium silicate solution to coat it with an interlayer. The coated plate is then rinsed with deionized water and dried at room temperature.
xe2x80x9cPGxe2x80x9d means xe2x80x9cpumice grained.xe2x80x9d The aluminum surface is first degreased, etched and subjected to a desmut step. The plate is then mechanically grained by subjecting it to a 30% pumice slurry at 30xc2x0 C., followed by a post-etching step and a desmut step. The grained plate is then anodized using DC current of about 8 A/cm2 for 30 seconds in an H2SO4 solution (280 g/liter) at 30xc2x0 C. The anodized plate is then coated with an interlayer.
xe2x80x9cG2Oxe2x80x9d is a printing plate substrate which is described in U.S. Pat. No. 5,368,974, the disclosure of which is incorporated herein by reference in its entirety.
xe2x80x9cCHBxe2x80x9d means chemical graining in a basic solution. After an aluminum substrate is subjected to a matte finishing process, a solution of 50 to 100 g/liter NaOH is used during graining at 50 to 70xc2x0 C. for 1 minute. The grained plate is then anodized using DC current of about 8 A/cm2 for 30 seconds in an H2SO4 solution (280 g/liter) at 30xc2x0 C. The anodized plate is then coated with a silicated interlayer.
xe2x80x9cPFxe2x80x9d substrate has a phosphate fluoride interlayer. The process solution contains sodium dihydrogen phosphate and sodium fluoride. The anodized substrate is treated in the solution at 70xc2x0 C. for a dwell time of 60 seconds, followed by a water rinse, and drying. The deposited dihydrogen phosphate is about 500 mg/m2.
A xe2x80x9cbasicxe2x80x9d surface will have a plurality of basic sites and acidic sites present, with the basic sites predominating to some degree. Similarly, an xe2x80x9cacidicxe2x80x9d surface will have a plurality of acidic sites and basic sites present, with the acidic sites predominating to some degree. It is known by one of ordinary skill in the art that the PG-Sil printing plate substrate appears to have a higher silicate site density than the DS-Sil printing plate substrate, and is more basic. It is also known that the G20 printing plate substrate exhibits less acidic character than AA printing plate substrates.
The oleophilic polymeric material of the fluid composition of the present invention that forms the ink-receiving layer is prepared from a mixture of cationic and anionic product polymers prepared from basic and acidic polymeric compounds, respectively. The cationic product polymer is prepared by partially or fully neutralizing the base groups of the basic polymeric compound with acid to give a product polymer that comprises the base groups and their cationic conjugate acid groups, or comprises solely the cationic conjugate acid groups. The anionic product polymer is prepared by partially or fully neutralizing the acid groups of the acidic polymeric compound with base to give a product polymer that comprises the acid groups and their anionic conjugate base groups, or comprises solely the anionic conjugate base groups.
A mixture of the cationic and anionic product polymers is used in the fluid composition to make long-lasting printing plates. The mixture enhances the adhesion of the polymeric material to the substrate. The cationic conjugate acid groups of one product polymer interact with the anionic conjugate base groups of the other product polymer of the mixture to enhance the binding of the polymers to the substrate. Without intending to be bound by any one particular theory, the ionic polymeric compounds undergo ionic crosslinking which increases the cohesive strength of the oleophilic layer on the substrate and increases the printing press run length. Thus, the chemical binding of the product polymers to each other provides strong adhesion of the ink-receiving layer, a more durable printing plate, and longer printing press runs. The conjugate acid and base groups of the product polymers can also react with the acid and basic sites of the substrate in ionic double exchange to bind the polymers to the substrate. These modes of chemical binding of the product polymers work in combination with the physico-chemical adsorption of the product polymers to the roughened substrate to provide strong adhesion of the ink-receiving layer.
Acids suitable for neutralizing the base groups of a basic polymeric compound conform to one of the formulae in the group consisting of H(CH2)nCOOH, and HOCHRCOOH, where R is xe2x80x94H, xe2x80x94CH3, or xe2x80x94CH2CH3, and n is from zero to six. Acids used in preferred embodiments are formic, acetic, lactic, and glycolic, while formic acid is especially preferred.
Bases suitable for neutralizing the acid groups of an acidic polymeric compound are selected from the group consisting of amines, ethanolamines, and the like. Bases used in preferred embodiments are ammonia and dimethylethanolamine, while ammonia is especially preferred.
Either the acidic or basic polymeric compounds can be a homopolymer, copolymer, terpolymer, and the like. The basic compound may also be a monomeric compound. By xe2x80x9ccopolymerxe2x80x9d we mean any polymer comprised of more than one type of monomer, prepared in a copolymerization. By xe2x80x9cterpolymerxe2x80x9d we mean a polymer consisting essentially of three types of monomers, prepared in a copolymerization. Thus, a copolymer can include a terpolymer.
In preferred embodiments, the basic polymeric compound is preferably selected from the group consisting of polymers and copolymers of 2-vinylpyridines, polymers and copolymers of 4-vinylpyridines, polymers and copolymers of diaminoethyl methacrylates, and mixtures thereof. These polymeric compounds comprise an amine moiety that can react with formic acid to produce conjugate acid groups attached to a polymer chain, to react with the substrate.
In preferred embodiments, the basic polymeric compound is a copolymer comprising a monomer having the following formula:
Rxe2x80x2Rxe2x80x3Nxe2x80x94Xxe2x80x94(CRxe2x80x2xe2x80x3)=CH2, 
wherein
Rxe2x80x2 is hydrogen or C1-5 branched or unbranched alkyl;
Rxe2x80x3 is C1-5 branched or unbranched alkyl;
Rxe2x80x2xe2x80x3 is hydrogen or methyl;
xe2x80x94Xxe2x80x94 is xe2x80x94C6H4xe2x80x94 or xe2x80x94(CH2)nxe2x80x94Qxe2x80x94(Cxe2x95x90O)xe2x80x94; 
wherein
n is 2 to 6; and
Q is oxygen or NH.
In preferred embodiments, the acidic polymeric compound is prepared from at least one monomer selected from the group consisting of acrylic acids, methacrylic acids, maleic acids, fumaric acids, and mixtures thereof. Acidic polymeric compounds prepared from these monomers include poly(acrylic acid)s, poly(methacrylic acid)s, poly(maleic acid)s, poly(fumaric acid)s, poly(styrene-co-acrylic acid)s, poly(styrene-co-maleic acid)s, poly(styrene-co-fumaric acid)s, and mixtures thereof. Further, but not limiting examples include polymers of ethylenically unsaturated sulfonic acids, polymers of sulfonated styrene, and copolymers thereof. These acidic polymeric compounds are made anionic by at least partially neutralizing with base, preferably ammonia, to create anionic groups from the acid groups of the polymeric compounds.
In a preferred embodiment, the acidic polymeric compound is polyacrylic acid and the basic polymeric compound is poly-4-vinylpyridine-co-butylmethacrylate. In an especially preferred embodiment, the acidic polymeric compound is polyacrylic acid, the basic polymeric compound is poly-2-vinylpyridine, the substrate is AA, and the precursor surfactant is FC-129.
The ink-receptive layer produced with the mixture of cationic and anionic product polymers has excellent adhesion to the substrate surface, and as set forth in further detail below, the resulting printing plate exhibits extended press run length. Advantageously, chemical development of the printing plate is not required.
The fluid composition comprising the oleophilic polymeric mixture is preferably applied by ink jetting to the substrate surface, typically by an ink jet printer using equipment and techniques which are well known to those skilled in the art. In this manner, the substrate is imaged so that after the fluid composition dries, an ink receptive layer is formed in the desired image on the surface of the substrate.
The fluid composition may comprise about 0.1 to 25 weight percent, preferably about 0.1 to 8 weight percent, and most preferably about 0.1 to 4 weight percent of the acidic polymeric compound, based upon the total weight of the fluid composition.
The fluid composition may comprise about 0.1 to 25 weight percent, preferably about 0.1 to 8 weight percent, and most preferably about 0.1 to 4 weight percent of the basic polymeric compound, based upon the total weight of the fluid composition.
Adsorbing a surfactant to a conventional printing plate substrate, prior to application of an ink receptive layer, can improve the image resolution achieved. Such a surfactant-pretreated substrate will be termed a xe2x80x9cprinting plate precursorxe2x80x9d herein. A printing plate may be prepared from the printing plate precursor by image-wise applying a fluid composition as described above to the substrate. In a preferred embodiment, the fluid composition is applied by means of an ink jet printer, and then dried to form an ink receptive layer in the form of the desired image. Advantageously, chemical development of the printing plate is not required.
Adhesion of the polymer from the fluid composition to the substrate after drying is not diminished substantially by the presence of the precursor plate surfactant, which tends only to slow the spreading of the droplet deposited by the ink jet nozzle. Thus, the precursor plate surfactant can increase resolution without reducing press run length. Surfactants that can be used for the precursor include alkyl tail surfactants, fluorosurfactants and siliconated surfactants.
Illustrative examples of alkyl tail surfactants include sodium dodecylsulfate, isopropylamine salts of an alkylarylsulfonate, sodium dioctyl succinate, sodium methyl cocoyl taurate, dodecylbenzene sulfonate, alkyl ether phosphoric acid, N-dodecylamine, dicocoamine, 1-aminoethyl-2-alkylimidazoline, 1-hydroxyethyl-2-alkylimidazoline, and cocoalkyl trimethyl quaternary ammonium chloride, polyethylene tridecyl ether phosphate, and the like.
Illustrative examples of fluorosurfactants useful in preferred embodiments of the present invention and their commercial trade names are set forth in Table 2.
ZONYL surfactants are commercially available from E. I. du Pont de Nemours and Co. and have a distribution of perfluoroalkyl chain length. FLUORAD surfactants are commercially available from 3M Company and have a narrow distribution of the hydrophobic chain length.
Illustrative siliconated surfactants include the following non-exhaustive listing: polyether modified poly-dimethyl-siloxane, silicone glycol, polyether modified dimethyl-polysiloxane copolymer, and polyether-polyester modified hydroxy functional polydimethyl-siloxane.
The precursor plate surfactant may be adsorbed onto the substrate by any conventional method, preferably by immersion of the substrate in an aqueous solution of the surfactant for a time, typically one minute, which is effective to permit adsorption of the surfactant upon the substrate. In a particularly preferred embodiment, any non-absorbed surfactant is then removed from the printing plate substrate surface. Preferably, the substrate is rinsed with water to remove non-adsorbed surfactant, then dried. The resulting printing plate precursor has a surfactant on at least one surface, in an amount effective to improve the resolution of printing.
An imaged substrate prepared by imagewise applying a fluid composition to a substrate could also be used, for example, as a precursor for a printed circuit board in which conductive metals are deposited onto the imaged substrate.
The following examples are given to illustrate preferred embodiments of the present invention and are not intended to limit the invention in any way. It should be understood that the present invention is not limited to the above-mentioned embodiments. Numerous modifications can be made by one skilled in the art having the benefits of the teachings given here. Such modifications should be taken as being encompassed within the scope of the present invention as set forth in the appended claims.